In an X-ray imaging system, X-rays that are generated by a focal spot of an X-ray source may be used to scan an object. A detector may be situated to face the X-ray source to detect X-rays that strike it. In response to the detected X-rays, the detector may generate signals that are used to reconstruct an image of the object.
During the scanning, it is desired to keep the relative position of the focal spot of the X-ray source to the detector (may be referred to as “relative position” in the following description) unchanged. However, the relative position may change with the working condition of the X-ray source. For example, when the temperature of the X-ray source changes, the relative position may change accordingly. Thereby, it is necessary to develop a system and method for determining the position of the focal spot of the X-ray source during the scanning, and correct the relative position (if necessary) for a subsequent processing (e.g., image reconstruction).